Electromagnetic sucker has been widely used for holding of material in machining work because of its fastness, firmness and convenience, It has replaced the conventional means such as chuck and the like. Though its operation is fast and accurate, the quality of structure of electromagnetic sucker has a great effect to machining quality. For instance, its deformation caused by change of temperature, corrosion of bronze by acidic machining fluid, stress resulted from its production, and strength of bronze soldered to core at room temperature do affect quality of electromagnetic sucker. As shown in FIG. 1, a fragmental prospective of a conventional electromagnetic sucker, the sucker (A) of the prior art is in the form a square iron sheet with traverse ribs (A.sub.1) and slots (A.sub.2) on the surface for contacting with the flange (B.sub.1) of a core (B) and the core (C.sub.1) of the base (C). Fabrication of such sucker is quite complicated, inner stress may exist at the corners of the ribs (A.sub.1) and affect the quality of the sucker (A) greatly. The core (B) and its separating plate (D) made of bronze are placed in each slot (A) of the sucker (A) and fixed there by soldering. However, hydrochloric acid remained on the surface of the sucker (A) after pickling, a necessary step in the preparation of sucker (A) can reach with the soldering agent chemically and hence adversely affect the soldering effect, the iron sheet will then rust. Moreover, as the core (B) and the bronze separating plate (D) are fitted into the slots (A.sub.2) at room temperature, there are different tightness from slot to slot, and inner stress exists. Upon change of temperature, precision of the surface of the sucker (A) is deteriorated, and then machining quality is adversely affected. Furthermore, complicated production procedure and waste of material are defects of such structure. Though there are kinds of improved suckers, such as that shown in FIG. 3, which were claimed as they are easy to make, save materials, lower production cost and improve precision, they can't eliminate the defects of the prior art. As shown in FIG. 3, such improved sucker is composed of convex iron core (m), separating plate (n) and intermediate element (o) by compression and soldering, and then fixed together by means of a frame (p). Such a structure has eliminated the need of forming ribs, but the fabrication of the frame (p) is very difficult, it is hard to control its dimension, and the same soldering process is used. Such a structure does not increase strength, and the defect of the prior art remains.